<!DOCTYPE html>
<html class="reftest-wait">
<title>
Transform transition and animation overridden by !important rule create
a stacking context
</title>
<style>
span {
  height: 100px;
  width: 100px;
  position: fixed;
  background: green;
  top: 50px;
}
@keyframes Transform100px {
  from, to { transform: translateX(100px); }
}
#test {
  width: 100px; height: 100px;
  background: blue;
  transform: translateX(200px) ! important;
  transition: transform 100s steps(1, start);
  animation: Transform100px 100s;
}
</style>
<span></span>
<div id="test"></div>
<script>
window.addEventListener("load", () => {
  var target = document.getElementById("test");
  getComputedStyle(target).transform;

  // Change the transform style to 'none'.
  target.style.setProperty("transform", "none", "important");
  // Important style is changed but there is a CSS animation,
  // so transition won't be visible and the CSS animation is overridden by
  // the !important rule. As a result transform style here should be 'none'
  // specified by the important rule, but we should create a stacking
  // context for it because there are animations.

  requestAnimationFrame(() => {
    document.documentElement.classList.remove("reftest-wait");
  });
});
</script>
